The subject matter disclosed herein relates to a premixing nozzle of a combustor used in a low emissions industrial gas turbine.
In combustion systems of low emissions gas turbine engines, sometimes referred to as Dry, Low NOx (DLN) combustors, premixed air and fuel are combusted within combustors that are disposed upstream from turbines in which mechanical energy is derived from the high temperature fluids produced by the combustion. Electrical energy is then generated from the mechanical energy and transmitted to electrical circuits. The combustors typically include fuel nozzles having premixing passages in which the air and fuel are mixed with one another. This premixing is done to decrease the peak flame temperatures in the combustor and reduce the formation of oxides of nitrogen (NOx) in the exhaust stream.
For fuel flexibility and power system availability, low emissions gas turbines are often equipped with a system to inject oil as a secondary or backup fuel in addition to the gas premixers. These oil injectors are typically inserted through the center of the gas premixers, such that the oil injection outlet communicates with the combustor reaction zone. Since the oil fuel is not evaporated and premixed with the air prior to combustion but is injected directly into the reaction zone, large quantities of water (several hundred thousand gallons per day in the case of a large power generation turbine) must be injected into the reaction zone to reduce the flame temperatures and the NOx emissions to the levels specified by regulators. Indeed, current methods often require that more water than fuel be directly injected to reach NOx levels near 42 ppm that are commonly expected when firing on oil fuel.
Also, in current breech-loaded/oil cartridge/gas premixer assemblies, concentric tubes, which are all rigidly supported on one end and free to move relative to one another on the far end are nested within one another. During turbine operations, the far ends of the tubes tend to vibrate in response to wide spectrum noise generated by the gas turbine engine and contact one another. The tubes and nozzle tip components are, therefore, prone to severe wear and fretting between mating parts.